One method for preheating glass batch involves feeding cold particulate glass batch raw materials into one end of a rotating heat transfer drum, and feeding hot media of larger particle size than the batch particles into the other end of the heat transfer drum. The glass batch moves in direct and immediate physical contact with the heated media, with the batch flowing from the cold end to the hot end of the drum and the media flowing from the hot end to the cold end of the drum. The heated particulate batch is removed from the hot end of the drum and the cooled media is removed from the cold end of the drum. Preferably, the heat transfer media is of a durable material and can be comprised of glass batch agglomerates, glass, ceramic material, steel, stainless steel, aluminum, or gravel. The media can be spherical in shape, and a usable example of such media is spherical ceramic balls, having a diameter of approximately 1 inch.
The media are heated by direct contact with hot gases from any suitable source, such as exhaust gases from a glass melting furnace, or hot gases heated in a heat exchanger by the exhaust gases from a glass-melting furnace. Typically, the media are heated in a hopper in which the media flows downwardly from a top media inlet to a bottom media outlet. The hot furnace exhaust gases typically are introduced into the hopper near the bottom of the hopper and flow upwardly to a hot gas outlet near the top of the hopper. In this manner, the gases are cooled, and the media is heated for use in the batch heat transfer process.
One of the problems of such preheating apparatus is that the cold balls entering the media heater are coated with batch dust, and the flow of hot furnace exhaust gases through the media in the hopper entrains some of the dust. For pollution control purposes this dust must be removed from the exhaust gases exhausted from the hopper through the hot gas outlet. It would be desirable to have the dust remain on the media for return to the batch heat exchanger with the heated media.
Another problem with such media heaters is that the cold media supply conduit cannot be efficiently sealed into an airtight condition. The typical designs of media heaters position the cold media inlet adjacent the hot gas exhaust outlet, thereby creating a significant negative pressure in the vicinity of the cold media inlet. The result is that a substantial portion of the gases exhausted through the hot gas outlet come directly from the relatively cold air flowing through the media inlet. This necessitates oversized exhaust fan and pollution control equipment to deal with the larger volume of gases withdrawn from the media heater.
Attempts have been made to provide airtight seals on the media inlet and outlet conduits, but such seals have been ineffective due to wear and tear and jamming of the equipment by media dust and media chips. The problem of undesireable exhaustion of cold air from the media inlet can be partially solved by reducing the pressure differential between the hot gas inlet and the hot gas outlet. This can be done by oversizing the diameter of the media heater. Such a solution is somewhat undesirable, however, in that an increased media heater diameter necessitates the employment of a larger volume of media, which considerably increases the expense and capital required for the entire operation.